DESCRIPTION

POE::Component::Client::HTTP is an HTTP user-agent for POE. It lets other sessions run while HTTP transactions are being processed, and it lets several HTTP transactions be processed in parallel.

It supports keep-alive through POE::Component::Client::Keepalive, which in turn uses POE::Component::Resolver for asynchronous IPv4 and IPv6 name resolution.

HTTP client components are not proper objects. Instead of being created, as most objects are, they are "spawned" as separate sessions. To avoid confusion (and hopefully not cause other confusion), they must be spawned with a spawn method, not created anew with a new one.

CONSTRUCTOR

spawn

PoCo::Client::HTTP's spawn method takes a few named parameters:

Agent => $user_agent_string

Agent => \@list_of_agents

If a UserAgent header is not present in the HTTP::Request, a random one will be used from those specified by the Agent parameter. If none are supplied, POE::Component::Client::HTTP will advertise itself to the server.

Agent may contain a reference to a list of user agents. If this is the case, PoCo::Client::HTTP will choose one of them at random for each request.

Alias => $session_alias

Alias sets the name by which the session will be known. If no alias is given, the component defaults to "weeble". The alias lets several sessions interact with HTTP components without keeping (or even knowing) hard references to them. It's possible to spawn several HTTP components with different names.

ConnectionManager => $poco_client_keepalive

ConnectionManager sets this component's connection pool manager. It expects the connection manager to be a reference to a POE::Component::Client::Keepalive object. The HTTP client component will call allocate() on the connection manager itself so you should not have done this already.

See POE::Component::Client::Keepalive for more information, including how to alter the connection manager's resolver configuration (for example, to force IPv6 or prefer it before IPv4).

CookieJar => $cookie_jar

CookieJar sets the component's cookie jar. It expects the cookie jar to be a reference to a HTTP::Cookies object.

From => $admin_address

From holds an e-mail address where the client's administrator and/or maintainer may be reached. It defaults to undef, which means no From header will be included in requests.

MaxSize => OCTETS

MaxSize specifies the largest response to accept from a server. The content of larger responses will be truncated to OCTET octets. This has been used to return the <head></head> section of web pages without the need to wade through <body></body>.

NoProxy => [ $host_1, $host_2, ..., $host_N ]

NoProxy => "host1,host2,hostN"

NoProxy specifies a list of server hosts that will not be proxied. It is useful for local hosts and hosts that do not properly support proxying. If NoProxy is not specified, a list will be taken from the NO_PROXY environment variable.

Specify BindAddr to bind all client sockets to a particular local address. The value of BindAddr will be passed through POE::Component::Client::Keepalive to POE::Wheel::SocketFactory (as bind_address). See that module's documentation for implementation details.

BindAddr => "12.34.56.78"

Protocol => $http_protocol_string

Protocol advertises the protocol that the client wishes to see. Under normal circumstances, it should be left to its default value: "HTTP/1.1".

Proxy => [ $proxy_host, $proxy_port ]

Proxy => $proxy_url

Proxy => $proxy_url,$proxy_url,...

Proxy specifies one or more proxy hosts that requests will be passed through. If not specified, proxy servers will be taken from the HTTP_PROXY (or http_proxy) environment variable. No proxying will occur unless Proxy is set or one of the environment variables exists.

The proxy can be specified either as a host and port, or as one or more URLs. Proxy URLs must specify the proxy port, even if it is 80.

Proxy => [ "127.0.0.1", 80 ],
Proxy => "http://127.0.0.1:80/",

Proxy may specify multiple proxies separated by commas. PoCo::Client::HTTP will choose proxies from this list at random. This is useful for load balancing requests through multiple gateways.

Proxy => "http://127.0.0.1:80/,http://127.0.0.1:81/",

Streaming => OCTETS

Streaming changes allows Client::HTTP to return large content in chunks (of OCTETS octets each) rather than combine the entire content into a single HTTP::Response object.

By default, Client::HTTP reads the entire content for a response into memory before returning an HTTP::Response object. This is obviously bad for applications like streaming MP3 clients, because they often fetch songs that never end. Yes, they go on and on, my friend.

When Streaming is set to nonzero, however, the response handler receives chunks of up to OCTETS octets apiece. The response handler accepts slightly different parameters in this case. ARG0 is also an HTTP::Response object but it does not contain response content, and ARG1 contains a a chunk of raw response content, or undef if the stream has ended.

FollowRedirects specifies how many redirects (e.g. 302 Moved) to follow. If not specified defaults to 0, and thus no redirection is followed. This maintains compatibility with the previous behavior, which was not to follow redirects at all.

If redirects are followed, a response chain should be built, and can be accessed through $response_object->previous(). See HTTP::Response for details here.

Timeout => $query_timeout

Timeout sets how long POE::Component::Client::HTTP has to process an application's request, in seconds. Timeout defaults to 180 (three minutes) if not specified.

It's important to note that the timeout begins when the component receives an application's request, not when it attempts to connect to the web server.

Timeouts may result from sending the component too many requests at once. Each request would need to be received and tracked in order. Consider this:

$_[KERNEL]->post(component => request => ...) for (1..15_000);

15,000 requests are queued together in one enormous bolus. The component would receive and initialize them in order. The first socket activity wouldn't arrive until the 15,000th request was set up. If that took longer than Timeout, then the requests that have waited too long would fail.

ConnectionManager's own timeout and concurrency limits also affect how many requests may be processed at once. For example, most of the 15,000 requests would wait in the connection manager's pool until sockets become available. Meanwhile, the Timeout would be counting down.

Applications may elect to control concurrency outside the component's Timeout. They may do so in a few ways.

The easiest way is to limit the initial number of requests to something more manageable. As responses arrive, the application should handle them and start new requests. This limits concurrency to the initial request count.

An application may also outsource job throttling to another module, such as POE::Component::JobQueue.

In any case, Timeout and ConnectionManager may be tuned to maximize timeouts and concurrency limits. This may help in some cases. Developers should be aware that doing so will increase memory usage. POE::Component::Client::HTTP and KeepAlive track requests in memory, while applications are free to keep pending requests on disk.

ACCEPTED EVENTS

Sessions communicate asynchronously with PoCo::Client::HTTP. They post requests to it, and it posts responses back.

request

Requests are posted to the component's "request" state. They include an HTTP::Request object which defines the request. For example:

Requests include the state to which responses will be posted. In the previous example, the handler for a 'response' state will be called with each HTTP response. The "progress" handler is optional and if installed, the component will provide progress metrics (see sample handler below). The "proxy" parameter is optional and if not defined, a default proxy will be used if configured. No proxy will be used if neither a default one nor a "proxy" parameter is defined.

pending_requests_count

There's also a pending_requests_count state that returns the number of requests currently being processed. To receive the return value, it must be invoked with $kernel->call().

my $count = $kernel->call('ua' => 'pending_requests_count');

NOTE: Sometimes the count might not be what you expected, because responses are currently in POE's queue and you haven't processed them. This could happen if you configure the ConnectionManager's concurrency to a high enough value.

cancel

Cancel a specific HTTP request. Requires a reference to the original request (blessed or stringified) so it knows which one to cancel. See "progress handler" below for notes on canceling streaming requests.

To cancel a request based on its blessed HTTP::Request object:

$kernel->post( component => cancel => $http_request );

To cancel a request based on its stringified HTTP::Request object:

$kernel->post( component => cancel => "$http_request" );

shutdown

Responds to all pending requests with 408 (request timeout), and then shuts down the component and all subcomponents.

SENT EVENTS

response handler

In addition to all the usual POE parameters, HTTP responses come with two list references:

my ($request_packet, $response_packet) = @_[ARG0, ARG1];

$request_packet contains a reference to the original HTTP::Request object. This is useful for matching responses back to the requests that generated them.

DEPRECATION WARNING

The third return argument (the raw octets received) has been deprecated. Instead of it, use the Streaming parameter to get chunks of content in the response handler.

REQUEST CALLBACKS

The HTTP::Request object passed to the request event can contain a CODE reference as content. This allows for sending large files without wasting memory. Your callback should return a chunk of data each time it is called, and an empty string when done. Don't forget to set the Content-Length header correctly. Example:

ENVIRONMENT

HTTP_PROXY sets the proxy server that Client::HTTP will forward requests through. NO_PROXY sets a list of hosts that will not be forwarded through a proxy.

See the Proxy and NoProxy constructor parameters for more information about these variables.

SEE ALSO

This component is built upon HTTP::Request, HTTP::Response, and POE. Please see its source code and the documentation for its foundation modules to learn more. If you want to use cookies, you'll need to read about HTTP::Cookies as well.

Also see the test program, t/01_request.t, in the PoCo::Client::HTTP distribution.